The periodic etching of tungsten surface induced by hydrogen ion irradiation

Abstract

BackgroundMetal tungsten (W) has a high melting point, low hydrogen solubility and high thermal conductivity. Therefore, it has been selected as one of the most promising plasma-facing materials for the future international thermonuclear experimental reactor (ITER).PurposeThis study aims to investigate the etching process of polycrystalline W induced by low energy hydrogen ion irradiation.MethodsPolycrystalline W materials were irradiated with 130 eV hydrogen ions. The irradiation damage behavior of W was researched by scanning electron microscopy (SEM), conductive atomic force microscopy (CAFM), Energy Dispersive Spectrometer (EDS) and nano indentation.ResultsThe investigates show that when the irradiation dose of H ions increases from 1.0×1024 ions∙m-2 to 1.5×1025 ions∙m-2, the surface of W material experiences a periodic evolution process from forming bubbles with H aggregation, the bubbles becoming bigger at grain boundaries, and gradually diffusing to the grain surface, until the W surface layer falls off due to the rupture of H bubbles. The irradiation dose required for one period of evolution is about (6.0~8.0)×1024 ions∙m-2. Nano indentation measurements show that the surface hardness of W material decreases after H ion irradiation. No impurities, especially elements of C and O, are detected on the W surface by EDS.ConclusionsIt is verified that the evolution of the unstable damage layer on the W surface induced by irradiations of low energy H ion is the main reason for the etching of W material. This work is very important for further understanding of the etching mechanism of W surface induced by H ion irradiation under the condition that the energy of irradiated H ion is lower than the sputtering threshold energy.

Keywords

• plasma
• tungsten
• h ions irradiation
• h bubble
• erosion